System for real-time adaptation to changes in display configuration

ABSTRACT

A hot-plugging capability for video devices is achieved by shifting the responsibility for recognizing changes in the configuration of a display environment from a computer&#39;s operating system to a device manager. When an input/output device is added to or removed from the computer system, an interrupt signal informs a device manager of the fact that a change in configuration has occurred. In response thereto, the device manager determines whether the changed component relates to the computer&#39;s display function. If so, the device manager makes a call to the computer&#39;s display manager, to inform it of the fact that the display configuration has changed. In response to this call, the display manager reconfigures the display space for the computer system and notifies clients as appropriate, to accommodate display features associated with the added component. With this change in the configuration of the display space, the added component becomes immediately available for use.

FIELD OF THE INVENTION

The present invention is directed to computer display systems, and moreparticularly to a display system which is capable of instantaneouslyaccommodating changes in the configuration of a computer system.

BACKGROUND OF THE INVENTION

As computers become more prevalent in everyday use, particularlypersonal type computers, users are employing them in a variety ofdifferent situations. Depending upon the particular situation, the usermay desire to change the configuration of the display devices connectedto the computer. For example, portable computers of the so-called laptopor notebook type have become increasingly popular because of their smallsize and light weight, making them suitable for use while traveling. Dueto the need to keep their dimensions to a minimum, the display screensbuilt into such computers are relatively small in size, and may offeronly limited display capabilities. Therefore, when using one of thesetypes of computers in an office environment, the user may connect it toa monitor having a larger display area and/or enhanced displaycapabilities. Such a connection might be made, for example, by means ofa docking station which enables the portable computer to be convenientlyconnected to a variety of peripheral devices, or by inserting a videocard in a PC Card slot.

Subsequently, the user might remove the added monitor, for example totake the computer home or to use it while traveling. In this situation,the built-in display screen must be used. In other words, the computermust route all information to be displayed to the built-in screen,rather than the port to which the external monitor was connected. Inaddition, the displayed information must be reformatted, or otherwiseprocessed, to accommodate the display parameters of the built-in device.

In the past, changes in the configuration of the computer system, suchas the addition or removal of display devices, only became effectiveupon a restart, or reboot, of the computer system. As part of itsinitial startup procedure, the computer's operating system detects thepresence of each device driver loaded on the system, and registers eachsuch detected driver to permit communications to be carried out betweenthe operating system and the device with which the driver is associated.If a new device and corresponding driver are added to the system afterthis initialization procedure, the driver is not registered with theoperating system, and therefore communications do not take place untilthe operating system goes through its initialization procedure again,e.g. upon the next reboot of the computer. Hence, if a user adds amonitor to the computer system, the monitor cannot be used to displayinformation generated by the computer until it has been rebooted.

U.S. Pat. No. 5,682,529 discloses a system for dynamically accommodatingchanges in the display configuration of a computer, without the need torestart the computer. In the system of this patent, changes can be madeto the display environment for a computer system while it is in a sleepmode, in which the computer's central processing unit is maintained in aminimal operating state. When the computer is “awakened” from this sleepmode, the system of the '529 patent enables the changed configuration tobe immediately recognized, and thereafter utilized in the display ofinformation generated by the computer.

As the capabilities offered by personal computers continue to expand,the opportunities for changing the configuration of computers grows in aconcomitant manner. In some situations, users may desire to have changesin the configuration of the computer's display environment becomeinstantaneously effective, without the need to restart the computer oreven place it in a sleep mode. For example, the user may create a slidepresentation on a notebook computer. During the course of a meeting, auser may desire to immediately display the slide presentation, byconnecting the computer to a suitable video projector, or the like. Itis desirable to be able to carry out this operation without the need tofirst put the computer to sleep, and thereby reduce the time needed tooperate within the changed configuration. It is an objective of thepresent invention, therefore, to expand upon the capabilities of thesystem of the '529 patent, by providing a display environment in whichso-called “hot plugging” of displays is possible, wherein a displaybecomes immediately available for use as soon as it is plugged into thecomputer system.

SUMMARY OF THE INVENTION

In accordance with the present invention, the foregoing objective isachieved by utilizing a device manager to automatically recognize andreact to changes in the configuration of a display environment, ratherthan wait for the computer's operating system to proactively determinethe status of the display environment, for example upon restarting. Whenan input/output device is added to or removed from the computer system,an interrupt signal informs the device manager of the fact that a changein configuration has occurred. In response thereto, the device managerdetermines whether the changed component relates to the computer'sdisplay function. For example, it may determine whether an added deviceis a video card. If so, the device manager makes a call to thecomputer's display manager, to inform it of the fact that the displayconfiguration has changed. In response to this call, the display managerreconfigures the display space for the computer system, to accommodatean additional frame buffer that is associated with the added component.With this change in the configuration of the display space, the addedcomponent becomes immediately available for use.

By means of this approach, the user can add a second monitor or otherhardware component to a computer and begin to use the monitor as soon asit has been connected, without the need to reboot the computer orotherwise interrupt its current operating state.

Further features and advantages of the invention are explained in detailhereinafter in the context of specific embodiments that are describedwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an overall display system architecture;

FIG. 2 illustrates an example of a display environment;

FIG. 3 is a block diagram of a display system architecture whichincludes plural video cards and display devices;

FIG. 4 is a block diagram illustrating the operation of the devicemanager; and

FIG. 5 is a flowchart illustrating the process by which changes in theconfiguration of the display environment become immediately available tothe user, in accordance with the principles of the invention.

DETAILED DESCRIPTION

The present invention is directed to the display environment of acomputer system. A block diagram of the overall architecture for adisplay environment is illustrated in FIG. 1. In this figure, hardwarecomponents of the computer system are illustrated above a dashed line10, and software components are depicted below the line. These softwarecomponents are stored in a suitable computer-readable medium, such as amagnetic disk, and loaded into the computer's working memory, i.e. RAM,for execution. The system can include display devices 12, e.g. monitors,LCD screens and/or plasma displays, although actual display devices neednot be physically present in order for the principles of the inventionto be operative. Each display device is connected to, and controlled by,a video card 14 which operates in accordance with video driver software16. Although depicted as being on a separate substrate, such as aprinted circuit board, the components of at least one video card couldbe incorporated with other components on a single substrate, such as thecomputer's motherboard.

One or more software programs, such as application programs 20, generateinformation to be displayed on the display devices. Examples of suchinformation include text, windows and other graphical objects, andcontrol structures such as menus and dialog boxes. This information ispresented to the display device through the computer's operating system18, which also generates its own information to be presented on thedisplay. The operating system communicates with the display devicethrough an associated display driver 13, which constitutes a softwarecomponent that corresponds to the hardware of the display device 12.

The operating system includes a display manager 22, which providescommunication between each of the software components, and dynamicallyconfigures the display devices 12. The communication between the varioussoftware components and the hardware devices takes place via theirassociated drivers, e.g. the video driver and the display driver. Inthis regard, many video displays have the capability to provideinformation regarding their available modes of operation and/or timingspecifications. Some displays, so-called “smart displays,” are capableof providing information about their modes of operation directly, forexample in response to inquiries. For these types of displays, thedisplay manager 22 communicates directly with the display device, bymeans of the display driver 13, over a communication channel 24. Thiscommunication channel can be a bus within the computer, a serial line,or any other suitable path for exchanging information between thedisplay manager and the display driver 13 of the display device.

In some cases, the display device may not be able to communicate itscapabilities directly. However, through the use of a lookup table or thelike, the display driver 13 can obtain information regarding thedisplay's capabilities, and provide them to the display manager.

The display manager also communicates with other parts of the operatingsystem 18 and the other software programs 20 that are running on thecomputer. For example, in response to operator commands, the operatingsystem can instruct the display manager to add a new device to a list ofactive displays, or remove a device therefrom. In response thereto, thedisplay manager informs the application programs 20 of the new displayconfigurations, to enable them to update their displayed informationaccordingly.

In one known implementation for computer systems, the displayenvironment can generally be considered to be defined by a globalcoordinate space 30, as depicted in FIG. 2. Objects and otherinformation to be displayed can be positioned anywhere within thisspace, as determined by the user and/or the software program thatgenerates the information. A reference point in this space, e.g. itsorigin or 0,0 coordinate point, is usually established with reference tosome object that is always present in the display. For instance, mostgraphical user interfaces include some type of menu bar or otherstructure which enables the user to access basic commands to control thecomputer. The device which displays this menu bar is known as the maindisplay device. If the computer system contains multiple displaydevices, only one of the devices is designated as the main device, evenif multiple devices contain the menu bar. The origin of the coordinatedisplay space is typically established with reference to the menu bar.For example, as illustrated in FIG. 2, the 0,0 point 38 in thecoordinate space can coincide with the top left corner of a menu bar 36.The positions of all objects and other information to be displayed inthe display space 30 are defined by their coordinates within this space.The operating system receives this coordinate information, for examplefrom the software programs 20 which generate the information, andprovides it to the display driver to cause the information to appear atthe appropriate place on the screen of the display device located at thecorresponding position in the display space.

In the example illustrated in FIG. 2, the display environment consistsof two display devices, 32 and 34, within the global display space 30. Amenu bar 36 is displayed at the top of the screen for the device 32,which is therefore the main display device. Accordingly, the origin 38of the display space coincides with the top left corner of the device32. As illustrated in FIG. 2, the user has caused some objects, e.g.windows 40, to be displayed on the device 32, and another object 42 tobe displayed on the device 34.

FIG. 3 illustrates the configuration of the computer system for theparticular example illustrated in FIG. 2, which includes two displaydevices. Each display device is connected to an associated video card,which includes a corresponding video driver. For the sake of simplicityin FIG. 3, the display drivers are not separately illustrated, but areassumed to be present within the system, in a manner analogous to thearrangement shown in FIG. 1. The embodiment of FIG. 3 includes two videocards 14 and 14′, respectively associated with the two video displaydevices 12 and 12′. Each of the video cards communicates with thedisplay manager 22, by means of its associated video driver 16 and 16′.

Among other components, each video card includes a frame buffer, e.g.random access memory, which stores the data for the image that isdisplayed on its associated display device 12. In essence, the displaymanager 22 assigns the frame buffer to a corresponding portion of theglobal coordinate space 30. In the example of FIG. 2, the two framebuffers are assigned to mutually exclusive portions of the global space.However, some or all of the portion assigned to one of the frame bufferscould overlap with the area assigned to the other frame buffer. In thiscase, the same image, or portion of an image, appears on both displaydevices.

At any given time, there could be only one video card connected to thecomputer, or both cards could be connected. Furthermore, in the case ofa network server or the like, it is possible that no video card would bepresent over certain periods of time. Even when both cards are present,only one of them may have a monitor or other display device connected toit at any particular point in time.

In the case of a conventional desktop or notebook computer system, oneof the video cards might be incorporated within the structure of thecomputer system, and may not be designed to be repeatedly inserted andremoved by the user. Additional video cards, however, might be capableof being easily inserted into and removed from the computer system. Forexample, the video card might be implemented in a removable card thatconforms to the PC Card standard. This standard defines the form factorfor relatively small, credit-card shaped I/O devices, which are designedto be easily inserted into and removed from computer housings, toprovide a computer with different capabilities. Included among the typesof I/O devices that can be embodied in such a card are modems, facsimiledevices, network interface cards, wireless communications devices andhard disk drives.

Devices of this type which conform to this standard, commonly known asPC Cards, are designed to be readily inserted and removed from thecomputer housing. The detection of the presence of such devices, as wellas their removal from the system, is handled by a portion of thecomputer's operating system that is referred to herein as a devicemanager. Referring to FIG. 4, when a PC Card 44 is inserted into thehousing of the computer, it actuates a switch 46, or equivalent sensordevice, which sends an interrupt signal IRQ to the device manager 48. Inresponse to this interrupt, the device manager determines the type ofdevice which has been inserted, and informs the operating system 18. Ina similar manner, whenever the PC Card is removed from the computerhousing, an interrupt is also sent to the device manager, which in turnnotifies the operating system that the device is no longer available.

Another type of change which can be made to the display configuration ofthe computer is the addition or removal of a display device. In theexample of FIG. 3, for instance, either one of the display devices 12 or12′ could be disconnected from its associated video card 14 or 14′.Furthermore, if only one display device is present, it could bedisconnected from one of the video cards 14 and connected to the othervideo card 14′. Whenever a change of this nature occurs, an interrupt issent to the device manager 48. For instance, the interrupt could begenerated by the video card, upon detecting that a display device hasbeen physically connected to or disconnected from it. Alternatively, theinterrupt could be provided by a bus that is capable of detecting such achange.

The addition or removal of other types of hardware can also result in achange in the display configuration of the computer system. For example,a graphics accelerator card can be added to the system by means of a PCCard slot. Again, upon the addition or removal of such a device, aninterrupt signal IRQ is sent to the device manager.

The present invention is particularly directed to the situation in whichthe device that is added to or removed from the computer system isrelated to the display function. In the past, it was necessary to rebootthe computer system in order for a change in video hardware to becomeeffective. More particularly, unless a reboot occurred, the operatingsystem was not prompted to undertake any action which would cause it todetect the presence of a new driver, resulting from the addition of anassociated hardware device. Hence, it was necessary for the user tointerrupt the operating state of the computer in order to utilize theadditional functionality provided by a newly added hardware. Once theoperating system became aware of the presence of the new driver, itcould notify the display manager to incorporate the presence of the newframe buffer.

In accordance with the present invention, however, the display systemcan be immediately responsive to the addition or removal of videohardware, so that the capabilities of a revised configuration can beemployed without the need to change the operating state of the computer.This functionality is accomplished by, in effect, bypassing the need tohave the operating system actively determine the addition or removal ofa display device. Rather, the notification of a change in theconfiguration of the display environment is provided directly to thedisplay manager, so that it can directly account for the presence orabsence of a particular video device.

To this end, whenever a PC Card is added to or removed from the computersystem, the device manager determines whether the card relates to adisplay function. A similar determination is made whenever an interruptis generated that indicates some other type of hardware has been addedor removed, e.g. a display monitor. In addition to, or in lieu ofinterrupts, other approaches can be employed to determine when a devicehas been added or removed. For example, the operating system canperiodically poll all of the computer system's I/O ports, to determinewhich devices are present and which ones might have been removed.

Referring to FIG. 5, upon receipt of an indication that there has been achange in configuration, the device manager first determines at step 50whether a device has been added or removed. If a device has been addedto the system, the device manager communicates with the device todetermine its type, at step 52, and stores data in a register regardingthe identity and type of the device. If the device responds with anindication that it is a video device, the device manager issues a callto the display manager 22, at step 54. Appropriate parameters can beincluded with the call, to indicate the type of device, the size of itsframe buffer (if applicable), its resolution, and the like.

In response to this information, the display manager carries out anumber of operations, depicted in Steps 56-64. First, it registers theadded hardware as a new device, along with the location of itsassociated drivers in memory, at step 56. In some cases, the driver mayalready be present in memory, but in an inactive state because thedevice was not connected to the system at the time of initial boot. Inthis case, the display manager switches the driver to an active state.

After registering the device, the display manager matches each displaydevice with an available frame buffer at step 58. If a new video card isinserted, for example, the display manager assigns a portion of theglobal coordinate space 30 to the frame buffer in the video card. If adisplay device is connected to that video card, the display managerassigns that device to the frame buffer for that card, so that theproper data is displayed on the device. If a display device isdisconnected from one video card and connected to a different videocard, the display manager moves objects within the global space 30 sothat they are presented to the appropriate frame buffer for the displaydevice. For example, the display manager can move user interface controlobjects which are specific to that display, such as brightness andcontrast controls, to the frame buffer associated with that display.Similarly, if the display has other attributes associated with it, suchas a certain name or designation, the display manager ensures that theyare directed to the proper frame buffer.

Once the display devices and frame buffers are matched up, the displaymanager consults a preferences file which indicates whether that devicewas connected to the system at some previous time. This file ispreferably stored in permanent memory, such as a hard disk, and updatedeach time a video device is added to or removed from the computer systemto change its configuration. The file stores the state of the displayjust prior to the change. For instance, it may store the location of themenu bar and all other objects on the desktop of the user interface,along with each device that made up the configuration. It can storerelevant operating parameters for the device as well, such as timingvalues, color depth, and the like. When a new device is added, thedisplay manager determines whether the changed configuration had existedpreviously, and if so it attempts to restore the display environment tothe state that existed the last time that configuration was present, atstep 60. For example, it might move the menu bar and certain icons tothe screen of a newly added display device, if they were previouslylocated on that device before it was disconnected, or set the timing ofan added frame buffer.

In addition to these actions, at step 62 the display manager can informcurrently executing programs of the presence of the new video device, asdescribed in detail in U.S. Pat. No. 5,682,529, the disclosure of whichis incorporated herein by reference. Furthermore, other software whichis not executing, but which relates to the new device, can be activated.For instance, if a graphics accelerator card is inserted in a PC Cardslot, the software associated with that card can be automaticallylaunched.

The display manager also functions at step 64 to rebuild or reconfigureresources that might be employed by the new device. For example, in somedisplay modes a table lookup operation is carried out to determine thecolors which are displayed on the monitor. Different applicationprograms may utilize different tables for this purpose. Typically, thewindow which is in the foreground of a display controls the particulartable that is used. Therefore, when windows are moved onto a new displaydevice, for instance in accordance with the preferences file, thedisplay manager rebuilds the color lookup table stored in the framebuffer for that device so that it corresponds to the appropriate window.

If the device manager determines at step 50 that a device has beenremoved from the system, rather than added, it determines at step 66whether the removed hardware was a video device, for example byreference to previously stored information which indicated the type ofcard inserted into each PC Card slot, or the like. If a determination ismade that the removed device was part of the video subsystem, the devicemanager sends a call to the display manager 22, at step 68, to inform itof this fact. In response thereto, the display manager updates thepreferences file at step 70, to record the relevant parameters thatpertain to the most recent configuration. In addition, the displaymanager can attempt to restore preferences that pertain to the newcondition. Thus, for example, if the computer system had two displaydevices and one was removed, the preferences file would be updated tostore the relevant data for the two-monitor configuration, and thensearched to determine whether it contains data for a one-monitorconfiguration. The display manager then rebuilds the displayconfiguration, at step 72. For example, if the removed device is a videocard, the display manager deletes the assignment of a portion of thedisplay space to the now-removed frame buffer. In concert with thisaction, the display manager can also function to move objects that werepreviously displayed on the removed display device to an area associatedwith a remaining display device, as described in greater detail in U.S.Pat. No. 5,682,529. If the removed device had executing softwareassociated with it, the display manager can cause the software to shutdown.

A special case can occur if all frame buffers, e.g. video cards, areremoved from the system. Since the frame buffer is a memory-mapped I/Odevice, a program or other device could attempt to address memory thatis no longer present. Typically, when such a situation occurs, theoperating system recognizes it as an error condition, and shuts down theprocess which attempted to address the non-existent memory. However, inthe system of the present invention, if an attempt is made to addressmemory in a video device, e.g. a frame buffer, the resulting errorcondition is treated as an interrupt. This interrupt is relayed to thedisplay manager to cause it to reconfigure the display environment, anddelete the assignment of display space to the frame buffer which is nolonger present.

Another action that can occur upon removal of a display device is tochange the operating mode of its display driver. More particularly, somedisplay devices can operate in one mode in which adjustment of controlbuttons, such as brightness and contrast controls, is accompanied byuser interface feedback, e.g. variation of a sliding scale on thedisplay. This operating mode requires communication with the computer'soperating system. In another operating mode, referred to as a remotemode, no such user feedback is provided. In the system of the presentinvention, when a display device is to be removed, the display managerinstructs its display driver to switch to the remote mode, so that noattempt is made to affect the user interface while the device is notpresent.

From the foregoing, it can be seen that the present invention provides ahot-plugging capability for video devices, that enables users toimmediately take advantage of changes in the display configuration of acomputer system, such as the addition of a new video card. Thisfunctionality is attained by providing notification of the changedconfiguration directly to the display manager, rather than waiting foran action that prompts the operating system to review the currentconfiguration, such as rebooting the computer.

It will be appreciated by those of ordinary skill in the art that thepresent invention can be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Forexample, while one embodiment of the invention has been described in thecontext of the insertion and removal of video cards that are embodied inPC Cards, it will be appreciated that the principles which underlie theinvention are not limited to this particular implementation. Rather, anyother suitable mechanism which accommodates the addition and removal ofa video device can benefit from the features of the present invention.The presently disclosed embodiments are therefore considered in allrespects to be illustrative, and not restrictive. The scope of theinvention is indicated by the appended claims, rather than the foregoingdescription, and all changes that come within the meaning and range ofequivalents thereof are intended to be embraced therein.

What is claimed is:
 1. A method for reconfiguring a computer system toaccommodate changes in a display environment, comprising the steps of:detecting the addition or removal of an input/output device in thecomputer system; determining whether an input/output device which hasbeen added or removed is a video device, in response to said detection;providing a notification to a display manager when a determination ismade that a video device has been added or removed; and modifying theallocation of display space to display devices via said display manager,in accordance with the addition or removal of a video device.
 2. Themethod of claim 1 wherein the video device comprises a video card thatincludes a frame buffer, and said modification step includes assigning aportion of the display space to the frame buffer of an added video card,or deleting the assignment of a portion of the display space to aremoved video card.
 3. The method of claim 1 wherein said displaymanager further carries out the step of storing a preferences file thatidentifies the status of displayed objects prior to a change in theconfiguration of a computer.
 4. The method of claim 3 wherein, upondetection of the addition of a video device, said display managerrepositions objects in said display space, in accordance with a statusstored in said preferences file.
 5. The method of claim 1 wherein saidvideo device is a display device, and said display manager carries outthe step of assigning a respective frame buffer, which corresponds to anallocated portion of the display space, to a corresponding displaydevice.
 6. The method of claim 1 wherein, upon detection of the additionof a video device, said display manager causes a software programassociated with the added device to be launched.
 7. The method of claim1 wherein said display manager further carries out the step ofreconfiguring a computer resource to correspond to the status of objectslocated in the display space.
 8. The method of claim 7 wherein saidcomputer resource is a color look-up table.
 9. The method of claim 1,further including the step of recognizing an error condition resultingfrom an attempt to address a frame buffer that has been removed,providing a notification to said display manager in response to saiderror condition, and deleting an allocation of display space to theremoved frame buffer.
 10. A system which provides hot-pluggingcapabilities for display devices, comprising: a video device including aframe buffer for storing data that defines an image to be displayed onan associated display device; a display manager which defines a displayspace and assigns a portion of said display space to said frame buffer,and which provides data for images to be displayed to said frame buffer;and a device manager which detects the addition or removal of a devicein a computer system, determines whether a device which has been addedor removed is a video device, and provides a notification of suchaddition or removal to the display manager when a video device isdetermined to have been added or removed, to cause the assignment of aportion of the display space to be modified in accordance with adetected addition or removal.
 11. The system of claim 10, wherein saiddisplay manager launches a software program associated with the videodevice in response to notification that the video device has been added.12. The system of claim 11 further including a preference file stored inmemory which indicates the status of objects being displayed when avideo device is removed.
 13. A system which provides hot-pluggingcapabilities for display devices, comprising: at least one display fordisplaying images; a display manager which defines a display space andassigns a portion of said display space to a display device, and whichprovides data for images to be displayed on said display device; and adevice manager which detects the addition or removal of a device in acomputer system, determines whether a device which has been added orremoved is a display device, and provides a notification of suchaddition or removal to the display manager when a display device isdetermined to have been added or removed, to cause the assignment of aportion of the display space to be modified in accordance with adetected addition or removal.
 14. The system of claim 13 furtherincluding a frame buffer which is associated with an assigned portion ofthe display space, and wherein said display manager modifies saidassignment by associating said frame buffer with said display device.15. The system of claim 13 further including a preference file stored inmemory which indicates the status of objects being displayed when adisplay device is removed.
 16. A computer-readable medium containing adevice manager program and a display manager program, wherein saiddevice manager program performs the steps of detecting the addition orremoval of an input/output device in a computer system, determiningwhether the input/output device is a video device, and providing anotification to the display manager program when a video device is addedor removed; and wherein said display manager performs the step of:modifying the allocation of display space to display devices in responseto said notification from the device manager.
 17. The computer-readablemedium of claim 16, wherein said display manager further performs thesteps of storing a preference file relating to the status of objectsappearing on a display device, and restoring objects to the statusstored in the preferences file when a video device is added.
 18. Thecomputer-readable medium of claim 16, wherein said display managerperforms the step of assigning a respective frame buffer to a displaydevice in response to said notification of an added display device, ordeleting the assignment of a respective frame buffer from said displaydevice in response to said notification of a removed display device. 19.The computer-readable medium of claim 16, wherein said display managerperforms the further step of launching a software program in response tosaid notification.
 20. The computer-readable medium of claim 16, whereinsaid display manager performs the further step of reconfiguring at leastone computer resource in accordance with the modification of the displayspace allocation.
 21. The computer-readable medium of claim 20, whereinsaid computer resource is a color look-up table.
 22. The method of claim3, wherein said preference file stores the video devices which make upthe configuration of the computer, and the locations of objectsdisplayed on said video devices.
 23. The method of claim 22, whereinsaid preferences file also stores operating parameters for said devices.24. A method for reconfiguring a computer system to accommodate changesin a display environment, comprising the steps of: detecting theaddition or removal of a video device in the computer system; providinga notification to a display manager that a video device has been addedor removed; modifying the allocation of display space to display devicesvia said display manager, in accordance with the addition or removal ofa video device; and reconfiguring a color look-up table to correspond tothe status of objects located in the display space.
 25. A system whichprovides hot-plugging capabilities for display devices, comprising: avideo device including a frame buffer for storing data that defines animage to be displayed on an associated display device; a display managerwhich defines a display space and assigns a portion of said displayspace to said frame buffer, and which provides data for images to bedisplayed to said frame buffer; a device manager which detects theaddition or removal of the video device to a computer system, andprovides a notification of such addition or removal to the displaymanager to cause the assignment of a portion of the display space to bemodified in accordance with a detected addition or removal; and meansresponsive to the removal of a video device for storing a preferencefile in memory which indicates the status of objects being displayed.26. The system of claim 25, wherein said display manager is responsiveto the addition or removal of a video device to restore displayedobjects to a status stored in said preference file which corresponds tothe configuration of the computer system after the video device is addedor removed.
 27. The system of claim 25, wherein said preference filestores the video devices which make up the configuration of thecomputer, and the locations of objects displayed on said video devices.28. The system of claim 27, wherein said preferences file also storesoperating parameters for said devices.
 29. A computer-readable mediumcontaining a device manager program and a display manager program,wherein said device manager program performs the steps of: detecting theaddition or removal of a video device in a computer system, andproviding a notification to the display manager program when a videodevice is added or removed; and wherein said display manager performsthe steps of: modifying the allocation of display space to displaydevices in response to said notification from the device manager, andstoring a preference file relating to the status of objects appearing ona display device, and restoring objects to the status stored in thepreferences file when a video device is added.
 30. The computer-readablemedium of claim 29, wherein said preference file stores the videodevices which make up the configuration of the computer, and thelocations of objects displayed on said video devices.
 31. Thecomputer-readable medium of claim 30, wherein said preferences file alsostores operating parameters for said devices.
 32. A computer-readablemedium containing a device manager program and a display managerprogram, wherein said device manager program performs the steps of:detecting the addition or removal of a video device in a computersystem, and providing a notification to the display manager program whena video device is added or removed; and wherein said display managerperforms the step of: modifying the allocation of display space todisplay devices in response to said notification from the devicemanager, and reconfiguring at least one computer resource in accordancewith the modification of the display space allocation.
 33. Thecomputer-readable medium of claim 32, wherein said computer resource isa color look-up table.